The use of microstrip radiators in large arrays for use thereof in communication systems has been increasing little by little as new materials and new techniques appear, which aside from resolving problems, have notably cheapened the manufacturing processes.
One of the main problems in space environment of antennas which operate in reception and transmission, is that one weld can generate a spurious signal in the reception strip as a passive intermodulation product (PIMP) of signals coming from the transmission band. The fact that in certain arrays there may be up to 6 welds per radiator makes it necessary to carry out a series of controls of non-existence of PIMP's by means of power tests in a vacuum chamber.
The studies carried out to avoid this matter have been basically directed towards eliminating welds, developing different alternatives to the feeding system, which have been grouped together under the generic name of excitation by electromagnetic coupling (EMC). However, this type of excitation without welds, which is still based on a coupling between the feeding line and the radiating element tends to entail the existence of isolated conductive masses, capable of causing electric discharges upon being at an uncontrolled potential. This problem incapacitates these radiators for their use in aircraft and space technologies.
A simple solution to this problem is to short-circuit the radiating element in points where the electric field is cancelled out, but this requires a well determined linear polarization of the radiated field, and except the including in the radiating system of a polarizing element, outside the radiator, this solution prevents the generating of circular polarization.